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What Is Psoriatic Arthritis?

Learn more about this form of inflammatory arthritis.

By Kerry Ludlam

Psoriatic arthritis (PsA) is an autoimmune disease – a form of inflammatory arthritis that can cause pain, swelling and sometimes damage to any joint in the body. It typically appears in people who have psoriasis, a chronic disease characterized by a scaly, reddish skin rash that usually appears on the elbows, knees and scalp.

A healthy immune system releases antibodies – agents that act as natural defenses against injury or disease-causing invaders – to heal the body in times of distress. But autoimmune diseases such as psoriatic arthritis turns the body against its own tissues, sending white blood cells to and inflaming the synovium – tissue that lines the joint capsule and produces synovial fluid, which lubricates the joint and keeps it moving smoothly. This inflammation causes the synovium to thicken, resulting in a puffy, swollen joint.

Over time, the synovium invades the cartilage, elastic tissue that covers the ends of the bones in a joint. The cartilage in turn erodes, causing bones to rub together. As the joint weakens, so do its the surrounding structures, such as muscles, ligaments and tendons. Because this joint damage can occur early in the disease process, diagnosing psoriatic arthritis as quickly as possible and treating it properly are important.

And while it’s most commonly associated with joints, psoriatic arthritis is a systemic condition, meaning that over time the inflammation that characterizes it can affect multiple joints and even organs.

What are the symptoms of psoriatic arthritis?

As with other forms of arthritis, symptoms of PsA vary among different people. Many symptoms are common to other forms of arthritis, making the disease tricky to diagnose. Here’s a look at the most common symptoms – and the other conditions that share them:

Painful, swollen joints: Psoriatic arthritis typically affects the ankle, knees, fingers, toes and lower back. However, the joint at the tip of the finger may swell, making it easy to confuse with gout, a form of inflammatory arthritis that typically affects only one joint.

Dactylitis: Many people with PsA experience this sausage-like swelling along the entire length of their fingers or toes. This symptom is one that helps differentiate psoriatic arthritis from rheumatoid arthritis (RA), in which the swelling is usually confined to a single joint.

Enthesitis: People with psoriatic arthritis often develop tenderness or pain where tendons or ligaments attach to bones. This commonly occurs at the heel (Achilles tendinitis) or the bottom of the foot (plantar fasciitis), but it can also occur in the elbow (tennis elbow). Each of these conditions could just as easily result from sports injuries or overuse as from psoriatic arthritis.

Psoriatic arthritis (PsA) is an autoimmune disease – a form of inflammatory arthritis that can cause pain, swelling and sometimes damage to any joint in the body. It typically appears in people who have psoriasis, a chronic disease characterized by a scaly, reddish skin rash that usually appears on the elbows, knees and scalp.

A healthy immune system releases antibodies – agents that act as natural defenses against injury or disease-causing invaders – to heal the body in times of distress. But autoimmune diseases such as psoriatic arthritis turns the body against its own tissues, sending white blood cells to and inflaming the synovium – tissue that lines the joint capsule and produces synovial fluid, which lubricates the joint and keeps it moving smoothly. This inflammation causes the synovium to thicken, resulting in a puffy, swollen joint.

Over time, the synovium invades the cartilage, elastic tissue that covers the ends of the bones in a joint. The cartilage in turn erodes, causing bones to rub together. As the joint weakens, so do its the surrounding structures, such as muscles, ligaments and tendons. Because this joint damage can occur early in the disease process, diagnosing psoriatic arthritis as quickly as possible and treating it properly are important.

And while it’s most commonly associated with joints, psoriatic arthritis is a systemic condition, meaning that over time the inflammation that characterizes it can affect multiple joints and even organs.

What are the symptoms of psoriatic arthritis?

As with other forms of arthritis, symptoms of PsA vary among different people. Many symptoms are common to other forms of arthritis, making the disease tricky to diagnose. Here’s a look at the most common symptoms – and the other conditions that share them:

Painful, swollen joints: Psoriatic arthritis typically affects the ankle, knees, fingers, toes and lower back. However, the joint at the tip of the finger may swell, making it easy to confuse with gout, a form of inflammatory arthritis that typically affects only one joint.

Dactylitis: Many people with PsA experience this sausage-like swelling along the entire length of their fingers or toes. This symptom is one that helps differentiate psoriatic arthritis from rheumatoid arthritis (RA), in which the swelling is usually confined to a single joint.

Enthesitis: People with psoriatic arthritis often develop tenderness or pain where tendons or ligaments attach to bones. This commonly occurs at the heel (Achilles tendinitis) or the bottom of the foot (plantar fasciitis), but it can also occur in the elbow (tennis elbow). Each of these conditions could just as easily result from sports injuries or overuse as from psoriatic arthritis.

Low back pain: Psoriatic arthritis often affects the sacroiliac joint, where the flared bones of the pelvis attach to the sacrum, the triangular bone at the base of the spine. Pain in the lower back is also a symptom of ankylosing spondylitis, a form of inflammatory arthritis that causes the vertebrae to fuse.

Nail changes: Nails may become pitted or infected-looking, or even lift from the nail bed entirely. This symptom, which is unique to psoriasis and psoriatic arthritis, actually helps doctors confirm a diagnosis.

Stiffness: Joints tend to be stiff either first thing in the morning or after a period of rest. This is another facet of PsA that makes it hard to properly diagnose; people with osteoarthritis often experience similar stiffness.

Fatigue: People with psoriatic arthritis often experience general feelings of fatigue. This symptom is a common feature of rheumatoid arthritis.

Reduced range of motion: The inability to move joints and limbs as freely as before is a sign of psoriatic arthritis – and most other forms of arthritis.

Conjunctivitis: Those with PsA may notice redness and pain in tissues surrounding the eyes.

Flares: Many people experience frequent periods of increased disease activity and symptoms, called flares, while others have only infrequent flares. This waxing and waning of symptoms is frequently seen with RA, as well.

Types of Psoriatic Arthritis

There are five types of psoriatic arthritis:

Symmetric: Accounting for about 50 percent of psoriatic arthritis cases, this type affects joints on both sides of the body at the same time. Symmetric psoriatic arthritis is similar to rheumatoid arthritis, causing joint pain and inflammation.

Asymmetric: Often mild, this type of PsA appears in 35 percent of people with the condition. It’s called asymmetric because it doesn’t appear in the same joints on both sides of the body.

Distal interphalangeal predominant: This type of psoriatic arthritis causes inflammation and stiffness near the ends of the fingers and toes, along with changes in toenails and fingernails such as pitting, white spots and even lifting from the nail bed.

Spondylitis: Pain and stiffness in the spine and neck are hallmarks of this form of PsA.

Arthritis mutilans: Though it’s considered the most severe form of PsA, arthritis mutilans affects only five percent of people who have the condition. It causes deformities in the small joints at the ends of the fingers and toes, and can dissolve them almost completely.

Who Gets Psoriatic Arthritis?

According to the Annals of Rheumatic Disease, between 6 and 42 percent of people who have psoriasis will develop psoriatic arthritis. The disease usually appears between the ages of 30 and 55 in people who have psoriasis, but it can be diagnosed during childhood. Unlike many autoimmune diseases, men and women are equally at risk for developing psoriatic arthritis. Approximately 70 percent of people who develop psoriatic arthritis have previously been diagnosed with psoriasis; another 15 percent develop skin and joint symptoms simultaneously.

What Causes Psoriatic Arthritis?

Like most forms of inflammatory arthritis, psoriatic arthritis has no known single cause. Researchers have found a strong genetic component to both psoriasis and psoriatic arthritis, as 40 percent of people who are diagnosed with these conditions also have family members affected by the disease.

Not everyone who has psoriasis develops psoriatic arthritis. Researchers believe PsA can be triggered by an infection or outside factor, such as extreme stress or injury, that sends the immune system of those already genetically predisposed toward the disease into overdrive.

How Is Psoriatic Arthritis Diagnosed?

Diagnosing psoriatic arthritis can be a difficult and time-consuming process because its symptoms frequently mimic those of other forms of inflammatory arthritis, such as rheumatoid arthritis and even gout. It can also be confused with osteoarthritis, the most common form of arthritis, even though it isn't inflammatory.

“Psoriatic arthritis is like a puzzle,” says Hayes Wilson, MD, chair of the division of rheumatology at Piedmont Hospital in Atlanta. “Many times pain or inflammation will occur in just one or two joints, or the psoriasis might be hidden in the scalp under the hair, so your doctor will need to work with you to put all of the pieces together.”

As part of the diagnostic process, your physician will likely refer you to a rheumatologist, a type of doctor who specializes in arthritis and musculoskeletal diseases. The rheumatologist will perform a physical exam, looking for swelling and inflammation of the joints. He’ll also check for signs of psoriasis on the skin or abnormalities on fingernails and toenails. Keep in mind that psoriasis isn’t always readily visible. It can hide in the scalp, behind your ears, in your belly button and in the groove between your buttocks.

The doctor may order X-rays to detect changes to the bones or joints. Blood can be examined for indicators of inflammation such as C-reactive protein and rheumatoid factor (an autoantibody that may or may not be present in people with rheumatoid arthritis, but is almost never present in people with psoriatic arthritis). Another test measures the sedimentation rate – the distance red blood cells fall in a test tube in one hour. The farther they fall, the greater the inflammation. Your doctor may also test joint fluid to exclude gout or infectious arthritis.

If you’re experiencing symptoms such as those noted above and your doctor doesn’t recommend sending you to a rheumatologist, ask about seeing one. Psoriatic arthritis is an uncommon disease, and many primary care doctors, along with quite a few dermatologists, just aren’t that familiar with it. Getting an accurate diagnosis lets your doctor select an appropriate treatment. Beginning treatment early in the course of the disease can mean improved quality of life for you now and less damage to your joints later on.